Among the engines to be installed on a motorcycle, there is the so-called "tandem V-engine", in which respective cylinders are inclined in the longitudinal direction. In this tandem v-engine, the power transmission mechanism of a drive system such as a reduction gear mechanism is disposed at the back of a crankshaft. According to the prior art, the front cylinder is inclined close to a horizontal position, whereas the rear cylinder is positioned close to an upright position so that it may be free from interference with the main shaft of the reduction gear mechanism. More specifically, the stud bolts for fixing the cylinder block of the rear cylinder to the crankcase have to be screwed deeply into the crankcase in order to have a sufficient strength, and the inner wall of the crankcase is made to protrude into the vicinity of the main shaft of the reduction gear mechanism in a manner to correspond to the positions, into which those stud bolts are screwed, whereby the reduction gear mounted on the main shaft, especially, the top gear having the maximum diameter has its outer circumference contacts with that protruding portion. In order to retain a sufficient clearance between that protruding portion and the reduction gear, therefore, it has been necessary to arrange the rear cylinder close to its upright position. With this construction, however, the height of the rear cylinder and accordingly the engine as a whole is so increased as to invite a disadvantage that the accommodation of the engine in the motorcycle having its engine installing space limited is deteriorated.
The present invention has been conceived in view of the background thus far described and contemplates to provide a V-engine which has its overall height reduced so that its installability upon a motorcycle can be improved.